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Direct digital receivers operating up to millimeter wave frequencies are desired for telecommunications, instrumentation, and surveillance, as analog received signals are digitized for high performance signal processing. The Analog-to-Digital Converter (ADC) is a vital component in detection systems. The ADC samples analog signals at discrete time intervals with a finite resolution and outputs a digital code to represent the signal. The Nyquist sampling time interval is determined by the ADC sample clock, fs, while the resolution is determined by the effective number of bits (ENOB) of the ADC. Timing jitters of electronic clocks have limited ENOB, as while self-forced opto-electronic oscillators have demonstrated a greater frequency stability as lows as 11fs at K-band. ADC performance requirements are identified in terms of Walden figure of merit (FOM). Integrated concept of opto-electronic based all-optical ADC has been introduced [3] as shown in Figure 1. A high signal to noise is maintained for all deflected angles. With current performance predictions of 9.4 ENOB at 40GSPS and under 230mW wall-plug power, the FoM is then 8.5 fJ/conv-step, which is better than the best reported FOM of 75 fJ/conv-step for an electrical ADC with speed of 2GSPS, 5.7 ENOB, and power of 2.3mW.
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